Hey folks.

I have read and read and read some more but I still need some help.

I just put in a new C68 AC/Heater Control unit in my 88 and it worked for all of 10 minutes - all doors were opening and all was as expected except for the AC which needs a freon top up and the air could have been hotter in heat and defrost modes.

Now the original symptoms are back - namely, I press buttons and nothing happens - no air blowing on any setting.

Diagnostic mode reveals nothing.

Should I be looking at changing the programmer unit (the black box) under the driver's side? What else can I do? Help would be appreciated.

Thanks!

 

Hard to deciper what you're saying.

What do you mean you push the buttons and nothing happens? Does the led light as you push each button?

Can you adjust the temperature with the heat and cool buttons?

Can you manually adjust the fan speed?

If the problem is the blower motor isn't working, it's controlled by the Blower Control Module located in the Evaporator housing.

With the ignition on and blower speed set to 10, unplug the two pin connector going into the blower motor. Use a volt meter and measure the voltage at the connector. One pin is ground and the other pin should measure around 12 volts.

 

1. Thanks for the reply. I appreciate it.
2. Sorry for the ambiguity. I'll try to clarify.

The fan speed numbers do work - that is, I can move from settings 1 to 10. Also, the temperature numbers work as well.

However, when I press any of the controls - for example, the AC, Bi-Level, Economy, Heater, or Defrost buttons, nothing happens. No air comes out.

What has me stumped is that all worked fine for about 10 minutes after swapping C68 units. Then nothing.

This morning, I started my car to check again and, lo and behold, it worked again.

Then, after I shut the car down and started it up again, the unit didn't work again!

This is what was happening with the old unit. Sometimes it worked; sometimes it didn't.

From reading so many other threads, I was wondering if it could be the programmer. Or could it be something else like, as you suggest, the blower control module?

What do you think?

Again, I do appreciate your input and thanks!

 

When the problem occurs, you need to measure the voltage at the blower motor.

If you look on the passenger side under the hood near the windshield washer bottle is the blower motor. On the bottom of the motor, unplug the connector and with the ignition on, select a function and manually set the fan speed to 10. You should measure 12 volts across the two pin connector.

If 12 volts is there and the blower motor doesn't run, the motor is bad.

If no 12 volts, you need to back track.

On top of the evaporator housing are two connectors.
One of them is a two pin connector with a large Red wire. You should measure 12 DC volts on that wire at all times.

The other connector is 4 pins. One of the wires is Brown.

As you vary the fan speed, the Brown wire voltage should also vary from 2.5 volts DC to around 7 volts DC.

This voltage comes from the AC/Heater Control Head and is applied to the input of the Blower Control Module. The output of the Blower Control Module drives the Blower Motor.

The Blower Control Module output will vary from 4 to 12 volts. (Purple wire) goes to the blower motor.

Also unplug the two connectors on top of the
Evaporator housing and verify the contacts are clean and the connector is not melted.

You can remove the Blower Control Module by removing the small bolts that hold it to the Evaporator housing. The module will pull right out.

 

Does air come out of any duct? Do you hear the blower running? What temp setting is displayed on the controls when you start it up and nothing is working? My guess is that you've got a bad ground - it runs to the driver's footwell - more info would help.

 

Hooked on Vettes:
Thanks. I will try what you suggest just in case but I'm leaning toward the programmer or a ground problem because the blower does work when the C68 Unit decides to function. I will let you know what the tests you suggest reveal, nevertheless.

SunCr:
I was hoping you would respond given your insight on other related threads.

When it functions, yes all is okay. The ground suggestion is worth a look, I suppose.

However, I was just messing around with the C68 unit with the ignition on and, when I switched my display to metric, the display was flashing and I heard clicking under the dash.

I tracked that clicking to the programmer. I disconnected it and the clicking went away, of course.

My Electrical Diagnosis Service Manual Supplement says the following:

"1. Check for flshing mode annunciator. For example, if there is a problem with the Ambient Sensor, In Car Sensor, or the Temperature Door Feedback Potentiometer, the EXT TEMP annunciator will flash for approximately 60 seconds upon ignition on."

Well, that's kind of what happened except that it was not the EXT TEMP that was flashing - it was the Temperature selector set at 32 degrees celsius accompanied as I said by the clicking noise. In fahrenheit mode, the flashing and clicking stops but the new unit functions only once in a while as did the old one.

So, bad ground? bad programmer?

What do you suggest? And thanks again! I do appreciate it.

 

I was thinking ground (or memory power), because when you remove either, it defaults to somewhere in the 70's and nothing works until the Programmer relearns the position of the temp door. An intermittent in either could cause this. Memory, if I remember correctly, is powered up from the Courtesy Clock Fuse. If anything else isn't working, that would be a prime choice. If everything else is working, then the ground, which runs all by it's lonesome to the left kick panel, is the prime pick.

Can't say I've heard a Programmer click. Not much (mechanically) to this little postcard though little ports are covered and uncovered to direct vacuum to the 4 HVAC solenoids. It also controls the Temp Door motor and if that linkage has broken, you might get some noise. However, that has zilch to do with anything else working, so I would guess that the Programmer, if that is making the noise, probably needs to be replaced.

 

Hooked on Vettes and SunCr ...

THANK YOU SO MUCH!

 

To SunCr:

1. Thanks for your input. I've installed a new programmer but the problem persists. When I swapped programmers, though, I noticed that one of the nubs (a Vacuum line?) didn't have a hose attached to it as did the other ones. Would that explain the vent doors not opening and closing properly now?

2. I'm eager to check the bad ground possibility but I need some clarification. If you could, I'd appreciate a quick walk-through.

Thanks again!

To Hooked on Vettes:

1. Thanks to you, too, for your advice. I've checked the blower motor voltage and the rest as you suggested and I think you led me in the right direction as well.

2. The blower motor does run with the ignition on but it doesn't read 12 volts. The brown wire and the purple wire as well don't measure up to the voltage scales you suggested.

3. Do I need to change the blower motor, the module, or both? What do you think?

Thanks again!

 

To check ground wires.

The Heater/AC Control Head has two black ground wires which go to G201. On the edge connector C Pin 7 and Pin 8. Both are 18 AWG Black wires.

If you use your ohm meter you should read zero ohms from each wire to the outside shell of the cigar lighter socket which is also grounded by G201. (If the cigar lighter works, the ground path is good to G201).

If you look at the electrical connector at the Heater/AC Programmer you'll see two Black wires. The larger wire is an18 AWG and is the ground wire. The other Black wire is a 20 AWG. Use your ohm meter and measure the resistance from the 18 AWG Black wire. You should read zero ohms to the outer shell of the cigar lighter.

The ground for the Blower Motor and Blower Control Module is G109. If you unplug the electrical connector to the Blower Motor you'll see one wire is Purple and the other is Black. You should measure zero ohms from the Black wire to the negative of the battery terminal.
If you don't, follow the Black wire and you'll see it is bolted to the top of the frame rail so it may need cleaning.

As for the vacuum hoses, the manual shows six.
Black Vacuum source
Red, Tan for A/C Defrost
Dark Blue Front
Pink Rear
Orange Outside air

 

Hooked on Vettes:

Simple AWESOME! I appreciate it to no end.

I'll get on that after golf tomorrow.

Baltimore is a bit out there from Toronto; but, if your in town, I've got a case of "real" beer with your name on it.

 

Just replaced my Blower Control Module on my 87 Vette with C68 due to the same type of failure. It would work one time and not the next, and then work again.

It is easy to replace!

Good luck,
Plasticman

 

Thanks, Plasticman and Hooked on Vettes.

I've tried 2 new modules but the problem persists.
Buddy at the parts store said he had similar problem and it turned out to be the wiring on the weatherpacks that connect to the module.



I'm stumped and would appreciate any other ideas.

Sorry for the delay but life got in the way.

 

Problem solved!

I gave the blower motor a couple of light taps with a screwdriver and, lo and behold, it kicked on. Shut the car down and no fan again so I tapped it again and it worked.

Gonna disassemble the Blower motor and clean the contacts to see if that fixes it or else I'll replace the Blower motor.

Thanks folks!

 

Last post to this thread.

Tried cleaning the blower motor contacts to no avail.

Put in a new blower motor and all is now good.

Thanks again, folks.